This invention relates to improved halogenated bis-imide flame retardants, to their manufacture and to compositions containing a flammable material and such halogenated bis-imides.
As is taught in U.S. Pat. No. 4,374,220, there are a multitude of halogenated bis-imides which are effective as flame retardants in composition with macromolecular flammable materials, e.g. polymers. These compositions are useful in making articles such as wire insulation coverings and electronic housings. Of these halogenated bis-imides, the alkylene(C.sub.1 -C.sub.6.sub.6)-(tetrabromophthalimide)s are especially commercially significant.
A presently used commercial route for producing alkylene (C.sub.1 -C.sub.6)-bis-(tetrabromophthalimide)s comprises reacting tetrabromophthalic anhydride with a diaminoalkane in the presence of water and an alkanoic acid to yield an alkylene-diammonium-bis-tetrabromophthalate). The reaction mass is then heated to about 210.degree. C. for a period of about 8 hours and the resultant desired alkylene(C.sub.1 -C.sub.6)-bis-(tetrabromophthalimide) product is recovered therefrom. This product is particularly useful as it has good thermal stability and resistance to UV degradation. However, the product has a yellow color which argues against its presence in compositions used for forming white articles. Also, the intensity of the yellow color can vary between product batches, which color variance makes it difficult for the article manufacturer to maintain consistency in the color of the articles produced. To overcome the yellow color problem, the art has provided processes which produce a white alkylene(C.sub.1 -C.sub.6)-bis-(tetrabromophthalimide).
U.S. Pat. No. 4,125,535 discloses a process for producing white alkylene(C.sub.1 -C.sub.6)-bis-(tetrabromophthalimide) by reacting tetrabromophthalic anhydride with diaminoalkane in a solvent system comprised of a liquid aromatic hydrocarbon and an alkanoic or aralkanoic acid.
Another process for producing this white bis-imide is disclosed in European Patent No. 0 023 420. This process comprises the bromination of alkylene(C.sub.1 -C.sub.6)-bis-(phthalimide) with a brominating agent, e.g. bromine, in 40-80% oleum. The product is white, however, it is not as thermally stable or as resistent to UV degradation as is the case for the before-described yellow alkylene(C.sub.1 -C.sub.6)-bis-(tetrabromophthalimide). Also it has now been demonstrated, that when compositions containing this white bis-imide are compression molded to form articles, the resultant article can be discolored by a yellow color or tint. This discoloration is believed to be due to a yellowing of this bis-imide as a result of its being exposed to the compression molding process conditions. Since injection molding processes are usually run under process conditions which are more harsh than those used in compression molding, it is expected, for this bis-imide, that the yellowing problem which would be encountered in injection molding would be at least as severe as that encountered in compression molding.
It is, therefore, an object of this invention to provide a white bis-imide, i.e. alkylene(C.sub.1 -C.sub.6)-bis-(tetrabromophthalimide) or bis-(tetrabromophthalimide), which has high thermal stability, resistance to UV degradation and which does not significantly contribute a yellow color to an article made from a composition containing such bis-imide.
It is also an object of this invention to provide a process for producing such a white bis-imide.
It is also an object of this invention to provide a composition which contains a macromolecular flammable constituent and a white bis-imide of the invention wherein the color of the composition is not significantly affected by a yellow color contribution from the bis-imide during the processing of the composition to form an article.
These and other objects are attained by oven curing alkylene(C.sub.1 -C.sub.6)-bis-(tetrabromophthalimide) or bis-(tetrabromophthalimide) which have been produced, respectively, by the bromination of alkylene(C.sub.1 -C.sub.6)-bis-(phthalimide) or bis-(phthalimide) with a brominating agent in the presence of oleum.